In recent years, several companies have developed systems that detect the presence of an object and in response, take some sort of action. For example, a passive infrared (PIR) sensor that is part of a security-lighting system detects the infrared radiation (IR) emitted in its surrounding environment and may cause the lights of the system to illuminate when changes to the environment, such as movement, are detected. This type of detection is passive in nature because the object in motion is not required to take any action, other than its normal interactions within the environment being monitored, for the PIR sensor to detect it. As another example, a system may emit signals, such as laser beams, for the detection of the movement of an object, which may be used to trigger an external system. Similar to the PIR sensor example, the interaction of the object is passive because the object is unmodified as it moves through the relevant area in a normal manner. That is, the object is not required to take any predetermined actions or move in any particular manner for the motion to be detected.
These passive systems, however, are not designed to provide any information about the objects that they detect. In particular, the PIR sensor and the motion-detector system are unable to track the object as it moves through the location being monitored. Such systems also fail to detect objects that are present but remain at rest for prolonged periods and cannot distinguish from one another multiple objects that may be detected in the same area. This latter event is particularly true if an object that initiated the original detection has left the area and a new and different object has entered the area at the same time or shortly thereafter.